Polymers comprising aromatic or aliphatic anhydrides have been studied extensively over the years for a variety of uses. For example, in the 1930s fibers comprising aliphatic polyanhydrides were prepared for use in the textile industry. In the mid 1950s, aromatic polyanhydrides were prepared with improved film and fiber forming properties. More recently, attempts have been made to synthesize polyanhydrides with greater thermal and hydrolytic stability and sustained drug release properties. U.S. Pat. Nos. 4,757,128 and 4,997,904 disclose the preparation of aromatic polyanhydrides with improved sustained drug release properties from pure, isolated prepolymers of diacids and acetic anhydride. A bioerodible controlled release device produced as a homogenous polymeric matrix from polyanhydrides with aliphatic bonds having weight average molecular weights greater than 20,000 and an intrinsic velocity greater than 0.3 dL/g and a biologically active substance is also described in U.S. Pat. No. 4,888,176. Another bioerodible matrix material for controlled delivery of bioactive compounds comprising polyanhydride polymers with a uniform distribution of aliphatic and aromatic residues is disclosed in U.S. Pat. No. 4,857,311.
Biocompatible and biodegradable aromatic polyanhydrides prepared from para-substituted bis-aromatic dicarboxylic acids for use in wound closure devices are disclosed in U.S. Pat. No. 5,264,540. However, these compounds exhibit high melt and glass transition temperatures and decreased solubility, thus making them difficult to process.
Polyanhydride polymeric matrices have also been described for use in orthopedic and dental applications. For example, U.S. Pat. No. 4,886,870 discloses a bioerodible article useful for prosthesis and implantation, which comprises a biocompatible, hydrophobic polyanhydride matrix. U.S. Pat. No. 5,902,599 also discloses biodegradable polymer networks for use in a variety of dental and orthopedic applications which are formed by polymerizing anhydride or diacid prepolymers. These polymers or matrices are useful for medical applications, either with or without an active agent as part of the diacid compound.